1. Field of the Invention
The invention relates to a control apparatus for an internal combustion engine having a fuel vapor treatment system that adjusts the amount of intake air through the cooperative control of the variable control of either or both of the lift amount of an intake valve and the working angle of the intake valve with the control in the degree of opening of a throttle valve.
2. Description of the Related Art
As a system adopted in internal combustion engines of vehicles and the like, systems that provide for the variable control of the lift amount and the working angle of engine valves (intake-exhaust valves) in accordance with the engine operation condition have recently been put into practical use (see, e.g., Japanese Patent Application Laid-Open Publication No. 2001-263015). An internal combustion engine provided with such a variable lift/working angle control system, the amount of intake air fed to a combustion chamber can be reduced by decreasing the lift amount or the working angle of the intake valves. By reducing the amount of intake air in this manner, rather than constricting the opening of the throttle valve, the pumping loss can be reduced; hence, it is possible to operate the engine with lower output (less amount of air) and therefore improve fuel economy.
Furthermore, a control apparatus that adjusts the amount of intake air through the cooperative control of the variable control of the lift amount/working angle, and the degree of opening of the throttle valve has been proposed.
Some vehicle-mounted internal combustion engines and the like adopt a fuel vapor treatment system in which fuel vapor produced in the fuel tank is removed by collecting the fuel vapor in a canister temporarily and later, at the appropriate time, releasing it from the canister into intake air. In this fuel vapor treatment system, the release of collected fuel vapor into an intake passageway is carried out through the use of the pressure of intake air (intake negative pressure).
In internal combustion engines adopting the variable lift/working angle control system, because the amount of intake air is reduced by decreasing the lift amount or the working angle of the engine valves as described above, the degree of opening of the throttle valve remains relatively large even during a low-load engine operation. That is, the internal combustion engine is operated in a state where the intake negative pressure is close to the atmospheric pressure. Therefore, the release of collected fuel vapor into the intake passageway sometimes becomes difficult, and securement of a necessary amount of release may become impossible.